creepage and clearance calculator

What creepage and clearance actually mean

When you place copper features on a PCB, the spacing between conductors is not just a routing problem; it is a safety and reliability problem. Clearance is the shortest distance through air between two conductive parts. Creepage is the shortest distance along an insulating surface between those same parts.

Air can break down during voltage surges, while contaminated surfaces can leak current and eventually carbon-track. That is why both distances are required and why one cannot simply replace the other.

Why these distances matter in real products

• Shock protection: Proper spacing reduces the chance of hazardous voltage bridging.
• Fire prevention: Insufficient spacing can cause sustained arcing and localized heating.
• Regulatory compliance: Certification labs evaluate spacing against applicable standards.
• Long-term reliability: Good creepage margins improve performance in humid and dirty environments.

How this calculator estimates the required spacing

This page uses a practical engineering estimate inspired by common tables used in IEC-style design workflows. The model applies:

• Voltage-based baseline values for air clearance and creepage.
• Pollution degree multipliers for harsher environments.
• Material group effects for surface tracking resistance (CTI class).
• Overvoltage category scaling to account for surge environment.
• Altitude correction for reduced air dielectric strength above 2000 m.
• Optional reinforced insulation factor and user-defined extra margin.

Internally, the tool computes an effective clearance stress voltage: V_clear = V_RMS × √2 for AC, and V_clear = V_DC for DC.

Step-by-step usage

1) Enter working voltage

Use the actual continuous operating voltage between isolated conductive parts.

2) Select pollution degree

PD2 is common for indoor consumer and office products. Use PD3 for more demanding industrial conditions with possible conductive contamination.

3) Select material group

FR-4 can span different CTI bins depending on laminate type. If unsure, choose a conservative group (such as IIIa or IIIb) until datasheets are confirmed.

4) Set overvoltage category and altitude

CAT III/CAT IV equipment sees larger transients. At higher altitude, needed clearance increases due to thinner air.

5) Apply margin and evaluate output

The calculator returns recommended minimum creepage and clearance in millimeters, then highlights the larger value as a practical pad-to-pad design starting point.

Practical PCB layout tips

• Use slots and cutouts to increase creepage without enlarging board size too much.
• Avoid sharp copper corners in high-voltage regions; rounded geometry helps reduce local field concentration.
• Keep flux residues low; contamination can reduce effective creepage performance.
• Use barriers, ribs, or coating where standards allow and where process control is strong.
• Document your spacing rationale in the design file for certification traceability.

Common mistakes engineers make

• Assuming low RMS means low surge stress.
• Ignoring altitude for globally shipped products.
• Treating conformal coating as an automatic standards waiver.
• Using generic FR-4 assumptions without checking CTI class.
• Forgetting that reinforced insulation usually requires roughly double the basic requirement.

Important disclaimer

This calculator is an educational and preliminary design aid. It is not a substitute for formal standards analysis or third-party safety certification. Always confirm final distances against the exact product standard, use condition, and certification body guidance.